Clausenamide, isolated from aqueous extract of dry leaves of Clausena lansium, a Chinese folk medicine, was found to have potent activity in enhancing LTP and show nootropic activity in animal tests. In order to discovery more potent stereoisomers and to analyze the relationship of structure-activity, the synthesis of 16 (8 pairs) optically pure stereoisomers of clausenamide with four chiral centers was achieved. The results of LTP assay showed that the nootropic activity of the stereoisomers of clausenamide is closely related to the configuration of stereoisomers.